1. Field of the Invention
The present invention relates to a process for the treatment of lesions by high energy radiation.
It relates more particularly to a process for the irradiation of cerebral lesions by use of a source of gamma rays associated with a collimator.
The invention also relates to a treatment device using the process.
2. Description of the Related Art
In gamma radiation apparatus used at present, the destruction of cerebral lesions treated by non-intrusive neurosurgery is obtained by the precise focusing of gamma radiation on the tumor to be treated. This destruction has to be done very carefully as to the doses of radiation received and absorbed by the healthy tissues.
According to a first known method, there is used a very intense single source whose radiation is focussed by a collimator in a slender cylindrical beam. The intensity of this single beam requires the application of a continuous orbital movement about the lesion to be treated so as to avoid the destruction of intermediate tissue traversed by the very high activity beam.
The continuous orbital movement is obtained by motorization of the heavy components which are the source carrier, the collimator and the associated shields.
According to a second known method, the risk of destruction of healthy tissue is reduced by the use of an assembly of sources whose individual intensity could not cause lesions in the healthy tissues. In return, the individual focussing of each of these sources generates conjointly an integrated dose sufficient for the treatment of the lesion itself.
The above method, as described for example in U.S. Pat. No. 4,780,898, requires the implantation of radioactive sources of very small diameter, generally of the order of a millimeter, and of their respective collimator. These collimators, incorporated in shields generally of lead, are typically about 200 in number and their machining requires long and costly operations. Moreover, the sources are spaced from the focal point and a great portion of their energy is converted to heat by the absorption of the radiation by the components themselves. As a result, only a small part of the radiation passes through the bore serving as a collimator and thus constitutes the only useful radiation for the treatment.
This method has drawbacks which on the one hand are technological connected to the geometry of the components and to the low output of the sources, and on the other hand economic by the absence of optimization of costly components.
There has also been studied an apparatus seeking to eliminate the major defects of the methods described above by limiting the telecontrol of the heaviest components and by decreasing the number of sources and their associated collimating device.
Research carried out has permitted controlling the relative displacement of the sources and of the patient as well as the energy necessary for point treatment of the tumors.
However, this point treatment, although it renders possible the treatment of the surface of a tumor by relative displacement, requires a relatively great duration of irradiation and does not satisfy completely the therapies which seek to obtain a lethal dose in a strictly limited volume corresponding to the dimensions of the tumor to be treated.